With the underground success of Diverse's excellent One A.M., Twista's Kamikaze entering the Billboard album chart at number one, and the wildly anticipated debut from Kanye West, Chicago hip-hop may be finally gaining some real momentum. But stuff's been happening here for years, and any number of local acts might have made it with better luck. One of these was Rubberoom: their only full-length, 1999's Architechnology, is a fierce underground classic shot through with millennial dread. But their New York label folded several weeks after the record's release, and the group barely stayed together long enough to see it reissued the following year on Sub Verse. Rubberoom producers Isle of Weight and Mr. Echoes (aka Fanum) resurfaced in 2002 as the Opus. Their first two releases (O.O.O. and First Contact, both on Ozone) are split between tracks featuring cameos from underground heroes (Slug, Aesop Rock, Murs, Mike Ladd) and ominous instrumentals in which the suffocating beats of the Rubberoom days are topped with dark atmospheric orchestral samples and spooky synth washes. But on the brand-new Breathing Lessons (Mush) the Opus have chosen their true path--aside from a single appearance by Chicago rapper Lord 360, it's an all-instrumental affair. The sound is pretty minimal, but the subtle shifts in texture and the hefty kick of the grooves keep it interesting. This gig is an unofficial release party for the new album that doubles as a Rubberoom reunion--MCs Lumba and Meta-Mo will rejoin their old producers for a few tracks (including some new stuff that may turn up on a Rubberoom EP planned for next year). It's also part of Chicago Rocks, a huge showcase of local underground hip-hop organized by the Molemen and featuring members of the Galapagos4 and Family Tree crews. Friday, February 6, 5:30 PM, Metro, 3730 N. Clark; 773-549-0203. The second Chicago Rocks show--with Brother Ali, Immortal Technique, and Iomos Marad--is Saturday at the Abbey Pub.